The present invention relates to a method of and a control apparatus for opening circuit breakers synchronously in a generator main circuit comprising multiple generator systems.
According to the latest knowledge in the Electrical Society Report of Year 1999 xe2x80x9c10th Power and Energy Group Conferencexe2x80x94Collection of Papers (Part B): Electric Power Devices and Phenomenaxe2x80x94B18 Circuit Breaker No. 464xe2x80x9d, it is reported that, when a short-circuit fault occurs and current waveform at a part of a power line construction having branch circuits (a construction having branches electrically) is observed (by calculation and analysis), a phenomenon of no current through current zero has occurred in an actual power system.
This report not only makes clear the occurrence mechanism of the phenomenon but also suggests countermeasures in an actual operation. For example, since the phenomenon of no current through current zero is likely to occur inevitably as a combined system characteristic of the characteristics of each electrical component, resulting from the plan and design of a power supply system, it is proposed to plan to coordinate the timing for turning off (opening synchronously) the AC circuit breakers on the power line on a precondition of occurrence of the phenomenon.
If a zero-less phenomenon occurs in a faulty current when a bypass protection failure signal is transferred from a means for judging whether a bypass protection device of a series compensator functions wrongly or will not function properly to a protection device for operating a circuit breaker, there is available a technique as disclosed in Japanese Patent Application Laid-Open No. 7-274380 (1995), which is a method for protecting a series compensating system from faults by controlling a circuit breaker so that a protection relay sends out a trip signal of the circuit breaker just in time for the timing when the zero-less phenomenon disappears. There is available another technique as disclosed in Japanese Patent Application Laid-Open No. 60-189124 (1985), which is a method that a resistance for inhibiting occurrence of the phenomenon of no current through current zero in an accidental current is provided in the generator main circuit so as to quicken the attenuation of DC component of the current sent out from a generator and allows the current to pass through current zero.
Although the above paper proposes a conception of countermeasures for preventing the phenomenon of no current through current zero, however, no concrete measures in practical operation is proposed.
Further, Japanese Patent Application Laid-Open Nos. 7-274380 (1995) and 60-189124 (1985) disclose measures against the phenomenon of no current through current zero as described above, but do not consider the following. That is, if a phenomenon of no current through current zero for many cycles occurs in a generation and transmission system, wherein multiple generator systems (group) are connected to a large-capacity system and these generator systems are operated in parallel, because a fault such as malfunction or grounding failure occurs in any one of the multiple generator systems, and even when circuit breakers of other sound generator systems are attempted to be shut down, it is likely to happen that the current not passing through current zero cannot be shut down and hence the generator main circuit cannot be protected surely due to this phenomenon of no current through current zero. The above Publications do not give any consideration to this point.
An object of the present invention is to provide a method of and a control apparatus for synchronous circuit opening of generator circuit breaker so as to be able to protect a generator main circuit from a phenomenon of no current through current zero at the time of the synchronous circuit opening of a circuit breaker of a sound generator system.
In order to achieve the above object, the present invention provides a method of synchronous circuit opening of a generator circuit breaker for a generator main circuit in which multiple generators are connected to a transmission system via circuit breakers so that a circuit breaker can be closed or opened synchronously; wherein, at the time when a circuit breaker installed in a generator main circuit is to be opened synchronously, if an electric signal for judging occurrence of an electrical fault in other generator main circuit is detected, opening of the circuit breaker synchronously is suspended for a specified length of time after the electric signal is detected.
The present invention also provides a method of synchronous circuit opening of a generator circuit breaker for a generator main circuit in which multiple generators are connected to a transmission system via circuit breakers so that a circuit breaker can be closed or opened synchronously; wherein, at the time when a circuit breaker installed in a generator main circuit is to be opened synchronously, the amplitude of AC current waveform of the generator output is amplified before the circuit breaker is opened synchronously so that the AC current reaches current zero, and then the circuit breaker is opened synchronously.
Besides, in order to achieve the above object, the present invention provides a control apparatus for synchronous circuit opening of a generator circuit breaker for a generator main circuit comprising multiple generator systems in which a generator is connected to a transmission system via circuit breakers; said multiple generator systems comprising a detecting apparatus for detecting occurrence of an electrical fault and a protection relay for shutting down the circuit breakers in case of an electrical fault; wherein, said control apparatus for synchronous circuit opening is provided with an interlock circuit which, at the time when a synchronous circuit opening command signal of a circuit breaker installed in a generator system is to be output, if an actuation signal of a protection relay installed in other generator system is output, suspends output of the synchronous circuit opening command signal for a specified length of time after the actuation signal is output.
The present invention also provides a control apparatus for synchronous circuit opening of a generator circuit breaker for a generator main circuit comprising multiple generator systems in which a generator is connected to a transmission system via circuit breakers; wherein at the time when a circuit breaker of a generator system to be opened of its circuit synchronously out of the multiple generator systems is to be opened synchronously, the amplitude of AC current waveform of the generator output is amplified by said control apparatus for synchronous circuit opening before the circuit breaker is opened synchronously so that the AC current reaches current zero, and then the circuit breaker is opened synchronously.